In the power supply architecture of the existing communication systems, due to the consideration of security and efficiency, an isolated Intermediate Bus Architecture IBA is extensively applied. In the architecture, the input voltage of the system is firstly converted into an intermediate voltage through an isolated Intermediate Bus Converter IBC, and then the intermediate voltage is converted into a voltage required by a load circuit through multiple post-stage non-isolated power supplies.
In order to adapt to different systems, an intermediate bus power supply is always required to adapt to a wider input voltage, in the case of processing a certain power, a power device thereof is required to simultaneously meet a high voltage stress, and a large current stress during low voltage input, therefore it is difficult to optimize the device selection. With regard to a common input voltage range 36˜75V of the communication systems, the power device is required to select a margin at least twice the rated power. Meanwhile, the power device as the bus power supply is required to process all power demands of one system, thus efficiency is also a foremost index, but selecting a device with a larger power margin always leads to lower efficiency and enlarges a power supply volume, which affects a power density index.
In the related art as shown in FIG. 1, a traditional switching power supply structure with voltage transformation is implemented with the Pulse Width Modulation PWM technology. When the input voltage range is wider, the pulse width duty ratio is varied greatly, so that energy storage elements such as an inductance and so on are required to constantly store and release more energy in the voltage conversion process, which causing that both volume and loss of the energy storage elements increase. The wide input voltage range also makes the power device need to simultaneously tolerate the high voltage stress during high voltage input and the large current stress during low voltage input, therefore, it is required to select a power device with a power much greater than the actual output power, which results in that both volume and loss of the power device increase. Therefore, the traditional switching power supply structure will lead to a problem of efficiency reduction and power density decline in the wide input voltage range.
In order to solve the problem of stress margin increase of the power device brought by the wide range of input voltage, a common scheme dealing with that is a two-stage structure as shown in FIG. 2, a non-isolated voltage stabilizing front-stage circuit and a transformer isolated post-stage circuit are included, so that the post stage is only required to deal with the fixed input voltage by the front-stage voltage stabilizing circuit, which avoids the stress problem brought by the wide input voltage range. However, the scheme does not solve the problem of larger variation of the front-stage duty ratio brought by the wide input voltage range. With regard to the buck switching power supply, the efficiency and the volume of energy storage elements can be optimal when the duty ratio is maximum, which correspondingly in such structure when the input voltage is lowest such as 36V but not the rated operational voltage. Therefore, both efficiency and volume cannot be optimal when the system is at the rated operational voltage such as 48V.
In order to deal with the problem of larger variation of the duty ratio brought by the wide range of input voltage, in the non-isolated switching power supply, the output non-inverting Buck-Boost topology as shown in FIG. 3 is usually adopted to effectively solve the problem, and it is widely applied to battery-powered terminal devices without isolation requirements. In the topology, the output voltage may be set as an intermediate value. When the input voltage is higher than a set value of the output value, the circuit works in a Buck mode. When the input voltage is lower than the set value of the output value, the circuit works in a Boost mode. Therefore, the duty ratio variation range may be halved.
The related art shown in FIG. 4 is a schematic diagram of the Buck-Boost topology added with an isolation function, an isolation part thereof is implemented by a traditional buck bridge circuit or other resonance circuits such as Logical Link Control circuit and so on. The circuit may achieve the advantage of narrow duty ratio variation range of the non-isolated Buck-Boost mentioned above, and meanwhile, the post-stage isolated circuit is also not required to deal with the stress problem of the power device brought by the wide range of input voltage, which is an application with higher efficiency in the related art.
But the technology is substantially equivalent to a composition of Buck+Boost+bridge isolated three-stage circuits, and a main application thereof is an isolated post stage with multiple different transformation ratios to form the division-ratio power supply architecture with various voltage outputs, and it employs relatively more power devices, which causes that the volume increase is greater when the power devices are used as a single power supply, and the power density is not high.
Therefore, the post-stage bridge circuit only plays a role of isolation or buck in the related art, but brings the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume.